Answer to Question #250052 in Microbiology for Hloni

Question

You have isolated several E. coli mutants: Mutant #1 has a point mutation in the -10 region of the promoter of a structural gene encoding an enzyme needed for synthesis of the amino acid serine. Mutant #2 has a mutation in the -35 region in the promoter of the same gene. Mutant #3 is a double mutant with mutations in both the -10 and -35 region of the promoter of the same gene. Only Mutant #3 is unable to make serine. Why do you think this is so?

Answer 1

When the mutant 1 has point mutation at-10 region, the promoter can bind at-35 consensus sequence and can initiate transcription. Similarly in mutant 2, point mutation is occurred at-35 region and promoter can bind at -10 region to initiate

transcription. In mutant 3, two point mutations had occurred at both-10 and-35 regions of consensus

sequences and promoter cannot bind at these mutated regions. Therefore,transcription does not

take place and mutant 3 could not make serine.